The present invention is directed generally to disk drives for data storage. More particularly, the invention concerns a motor control system for reducing spindle power and acoustic noise in such drives.
The use of multi-phase brushless d.c. motors for powering computer disk drives is well known. In such drives, a plurality of stator coil elements are configured on a stationary substrate having a central axis about which the coil elements are uniformly arranged. A rotor assembly having a plurality of permanent magnets formed thereon rotates around the central axis, above the stator coils. The coils are periodically energized in order to induce rotational movement in the rotor assembly. Unlike conventional brush motors having mechanical brushes to commutate the stator coils, brushless or commutator-free motors used in disk drives are self commutating. They rely on magnetic or optical sensors and electronic circuitry to provide output commutation signals corresponding to the angular position and rotational speed of the rotor element.
In contrast to conventional d.c. motors, brushless motors tend to generate unwanted noise and vibration as a result of excessive spindle power consumption. Moreover, whereas conventional d.c. motors have many commutator bars providing a relatively smooth torque output curve, brushless motors have relatively few phases driving the rotor. The relatively long duration of passage of the rotor over the stator results in significant torque ripple, which in turn causes acoustic noise and vibration, The structural components of the drive may also generate acoustic noise and vibration, as a result of structural resonance for example.
Accordingly, there is an evident need in the art for an improved brushless d.c. motor control system for a disk drive. What is required is an apparatus and method that efficiently reduces spindle power and accoustic noise and vibration caused by excessive power consumption, torque ripple and physical drive properties.